1. Field of the Invention
The present invention relates to a process and apparatus for molding cellulosic fibers and the product produced by the process and, in particular, a process for molding recycled cellulosic fibers.
2. Description of the Related Art
Processes for molding mixtures of cellulosic fibers and binders are known. Methods for applying a resinous binder to cellulosic fibers typically include: a wet method and a dry method. The wet method of applying the binder requires dissolving the binder in a solvent, such as water, and spraying the binder onto the fibers. In the dry method, the dry resinous binder is blended with the cellulosic fibers without the addition of a solvent, prior to forming a molded mat or part. In each of these methods the cellulosic fibers are laid by air into a mold.
Several problems are associated with the wet method. The solvent must typically be removed from the fibers prior to entraining the fibers into an air stream as the fibers are placed in a mold. The removal of the solvent disadvantageously results in removal and thus waste of part of the binder making it difficult to properly include the correct amount of binder. Also, wet fibers are difficult to process as they tend to agglomerate.
The dry method does not involve these drawbacks of the wet method and in that regard is the preferable method.
One type of the dry method, as disclosed in Caron et al., U.S. Pat. No. 3,230,287, is a conventional air-laying process for manufacturing moldable fibrous panels. Caron et al. disclose air-laying wood fibers mixed with a thermoplastic or thermosetting resin. The Caron et al. process produces a moldable fibrous mat of uniform thickness.
Among the problems associated with the here-to-for conventional dry air-laying methods is that the dry resin binder will separate from the cellulosic fibers during the air-laying process. To compensate for this separation, excess resin is required in the attempt to achieve the desired resin content in the finished fiber and resin mix. However, the use of excess resin is likely to result in the nonuniform distribution of the resin, which results in deficient mechanical properties of the finished product.
One method proposed for overcoming the problem of the resin separating from the cellulosic fibers is to simultaneously feed cellulosic material and a dry resin-containing air stream to a comminuting means. Mtangi et al., U.S. Pat. No. 4,647,324, disclose such a simultaneous feeding process whereby the resin and cellulosic material are both retained in the comminuting means for a sufficient period of time to avoid separation so that the resin is uniformly deposited over the surface of the cellulosic particles during air-laying into a fiber web. The Mtangi et al. web is then molded at pressures of 180-250 psig into a molded article having a uniform distribution of resin.
A disadvantage of the Mtangi et al. process is that the mixture of dry resin and cellulosic material has little or no flow properties and is, therefore, very difficult to properly place into a mold and to then press into a molded part from the flat fiber web.
Another known approach involves a two-step dry process for producing a unitary-rigid composite board from shredded paper containing thermoplastic material. Downs et al., U.S. Pat. No. 3,718,536, disclose the initial formation of a pre-form by heating a batt of shredded paper containing thermoplastic material to 300.degree.-350.degree. F., which is above the softening temperature of the thermoplastic material, and thereafter subjecting the batt to pressures of 10-60 psig. The Downs et al. process subsequently presses the pre-form to its desired density having a uniform distribution of thermoplastic material. Downs et al. fails to teach, however, the formation of a molded part.
Thus, a molding process and apparatus have yet to be provided that enable the formation of a molded part of cellulosic fibers and a resinous binder.